Just saw this thread now, but I made a caffeinated IPA last year similar to the original post. I got a bunch of caffeine powder from a buddy and aimed for 150mg per 12oz. beer and used it in an entire 5 gallon batch. I think it was around 7.5%, 70 IBUs and I dry hopped it pretty good.
I think my fermentation schedule went as follows:
Primary for about 2 weeks
Second with 2oz. hops (forget what I used) for 2 weeks
Third with 2oz. hops, 1.5oz. oak chips, and caffeine for 2-3 weeks
I played around with the caffeine powder a lot to see how it was affected by different tempertaures. I found that it dissolved well in hot water but if it was cooled too fast it would solidify again. So I dissolved it on a hot/stir plate, brought it to a boil, then let it cool to room temperature naturally and then dumped it into the third fermenter.
It turned out pretty well and I found the taste of the caffeine to mellow with age. If I had more than two of these it would upset my stomach, but I had a buddy drink 3-4 and he had a great time.